The present invention generally relates to an apparatus for simultaneously detecting a plurality of discrete laser modulation frequencies and, in particular relates to one such apparatus having a detector circuit with means for canceling background radiation.
In modern warfare many weapons rely on laser beams to acquire and track targets. The use of lasers in this fashion has numerous advantages among which is the difficulty of the target to detect the fact that it has been targeted. Hence, there is considerable time and expense being dedicated to laser detection. It is known that, because of the nature of lasers, laser targeting systems either operate at only a limited number of frequencies or, due to the modulation techniques conventionally employed, the frequencies are difficult to change once a weapon is in production.
At the present time, laser detection systems require expensive passive and analog circuitry, as well as digital signal processing equipment. The main disadvantage of conventional systems is the expense of obtaining high performance in the presence of background light radiation. For example, since most lasers operate at visible light frequencies, the detection of the presence of a laser in daylight is difficult due to the presence of sunlight. Sunlight causes a very strong background against which to discriminate a laser. To accomplish such discrimination with a sufficient signal to noise ratio to be useful, expensive optical components and circuitry and techniques, such as those cited above, are required.
Consequently, it is highly desirable to provide a circuit that overcomes the difficulties of laser light discrimination from background radiation using relatively inexpensive circuit components and techniques.